For head-mounted display devices, a large viewing field angle can enhance the sense of immersion and thus improve the entertainment effect. However, the field curvature and the magnification chromatic difference caused by the increase of the viewing field angle will seriously affect the system imaging quality. The conventional eyepiece system requires a lot of lenses to correct the aberration, and conventional optical glasses have a high weight, which increases the burden of head-mounted devices on human body. Thus, the eyepieces of the head-mounted systems with a large viewing field need a more novel and simple design.
In addition, for crowds of nearsightedness or farsightedness, the current fully-fixed head-mounted system cannot meet their demands, because when not wearing glasses, the user will feel that the image is blurry due to the nearsightedness or farsightedness. Although the defocus relative to the retina caused by nearsightedness or farsightedness can be compensated for when the glasses are worn, it is not convenient or comfortable. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.